CN1483136A

CN1483136A - Improved linear variable differential transformer for high-accuracy posotion survey

Info

Publication number: CN1483136A
Application number: CNA018198120A
Authority: CN
Inventors: R・普罗克施; R·普罗克施; 夫兰; J·克利夫兰; 锌; D·博切克
Original assignee: ACELLEM RESEARCH PTY Ltd
Current assignee: ACELLEM RESEARCH PTY Ltd
Priority date: 2000-11-30
Filing date: 2001-11-30
Publication date: 2004-03-17
Also published as: US20060192551A1; KR100794976B1; EP1340040A2; US20060186878A1; US20040075428A1; KR20030084903A; JP2008102144A; US7233140B2; US20060202683A1; WO2002044647A3; US20060186877A1; US7038443B2; US7372254B2; US7459904B2; US20020175677A1; US20070200559A1; JP2004523737A; US20060186876A1; US7262592B2; WO2002044647A2

Abstract

A transducer that reduces noise, increases sensitivity, and improves the time response of a linear variable differential transformer (LVDT). The device replaces the primary coil and the high permeability ferromagnetic core of conventional LVDTs with a primary wound around a moving non-ferromagnetic core. In addition to reducing or eliminating Barkhausen noise, this approach reduced or eliminated a number of other undesirable effects in conventional LVDTs including excessive eddy current heating in the core, non-linearities associated with high permeability materials and the length scale of the flux circuit. These improvements are coupled with improved LVDT signal conditioning circuitry. The device is also an actuator and may be used to convert differential voltages into force. Devices with these improvements have numerous applications, including molecular force measurements, atomic force microscopy and manipulation technology, lithographic manufacturing, nanometer scale surface profiling and other aspects of nanotechnology.

Description

Be used for the improvement linear variable differential transformer that high precision position is measured

Technical field

The present invention relates to minimum mechanical shift (reaching Subnano-class for a short time) is transformed into differential voltage many devices of (with vice versa).

Background technology

Early stage in eighties of last century, it is linear variable differential transformer (LVDT) that mechanical shift is transformed into a kind of position transducer that differential voltage (with vice versa) utilized.Described conventional commercial LVDT (Part No. 50-00-005XA, Seotech company limited, North Hills, PA, the U.S.) in Fig. 1, that one moves, ferromagnetic core 1 is differentially from primary coil 2 coupling magnetic flux to two secondary coil 3 and 4.Pass through primary coil by oscillator 5 drive currents.When the core position changed with respect to secondary coil, magnetic flux is coupled to two secondary coils to be changed.These voltages be with differential amplifier 6 amplify and with Signal Regulation electronic device 7 with the voltage direct proportion be transformed into the core displacement.For little displacement, signal is linear.The motion core is mechanically connected to by the relevant object of axle 8.These coils are placed in the housing through being commonly used for magnetic shielding 9.Because core 1 is soft ferromagnetic on magnetic, often expectation shields it to coming from the outside magnetic field.Best commercial LVDT is limited to when the 100Hz bandwidth to be operated in ± 2.5nm spatial resolution (the accurate model AB-01 of Lion, Lion Micronics Inc., St, Paul, MN, the U.S.) in the 500nm scope.

The another kind of position transducer that mechanical shift can be transformed into differential voltage uses capacitance technology.Although when using LVDT, depend on the Signal Regulation electricity economize on electricity road of same model, the commercial capacitive transducer of working in being similar to the situation of commercial LVDT has surpassed almost order of magnitude of LVDT performance.(for example, see Physik Instrumente＜physical apparatus〉catalogue, 2001 editions).Even they are to be difficult to work together and more expensive in fact (because requiring create conditions) more, therefore, capacitive transducer often is the element that could select in these application that require highest measurement resolution and bandwidth.

Because theirs is easy and low-cost, so determine the reason that limits and how to overcome these restrictive conditions in the LVDT resolving power, this is the most useful.When being provided with more completely when following, we conclude that in traditional LVDT resolving power resolving power restriction is the Barkhausen noise in ferromagnetic core.The good noise of Bark is the unexpected jump in the magnetic state of ferromagnetic material (Bozorth) and naming.In ferromagnetic material, these defectives cause the preferential pinned special position of these neticdomain walls.Because heat energy or external magnetic field, neticdomain wall can be pegged by disengaging then.When this takes place, neticdomain wall will jump to another metastable position of pegging, and cause unexpected variation in whole magnetic state of material.Generally, when from pin magnet material formation LVDT core, because the flux change of Barkhausen noise will can not offset in the variate of two secondary coils.This unmatched noise directly causes the noise in the core position signalling.Also have, the unexpected variation in the magnetic state of core can cause some variations aspect the transducer sensitivity, causes position noise again.

In LVDT in the past, some schemes are arranged, comprise increasing current driving primary coil and in core, use unbodied magnetic material that (Meydan, I. wait the people for reducing Barkhausen's (with electricity) noise; Hristoforou, E. waits the people; And Midgley, G.W. waits the people).The proper drive current that increases will increase signal to noise ratio (S/N ratio) in traditional electronic device, but it is invalid when handling Barkhausen noise, because it produces bigger oscillating magnetic field, can expel successively like this that the neticdomain wall of pegging is easier to cause increasing locational noise.Use unbodied magnetic material for reducing Barkhausen noise to minimum degree, having illustrated, but be invalid eventually, because Barkhausen noise is the fundamental property of ferromagnetic material.

Though do not understand the generation of Barkhausen noise, some unconventional LVDT design replaces the ferromagnetic core of traditional LVDT to want to eliminate this effect with air-core.These are by Ellis and Walstrom (United States Patent (USP) .3 for use the sensor that designs in high magnetic field, 030,085) described, by Kimura (United States Patent (USP) .4,634,126) pin of being narrated-ball mechanical hook-up and by Neff (United States Patent (USP) s.2,364,237 and 2,452,862) and the various mechanical metrology applications of Snow (United States Patent (USP) s.2,503,851) narration.Gauge by Snow narration uses incentive program, wherein two main coils be energized rather than one be energized.A coil drives at 180 degree places from another coil, produces oscillating magnetic field from two main coils and trends towards cancelling out each other.Single air-core in central authorities is used as detecting device.This with by we with other normally used method and different incentive programs.In essence, primary coil and secondary coil are opposite.Can expect that from reciprocal theorem (for example, seeing Bertram, H.N., magnetic recording theory, Cambridge publishing company, 1994) electro permanent magnetic of two positions of a kind of situation is identical.Yet, same some necessary difference that exists on the noiseproof feature that interrelates with Signal Regulation.Generally, be widely littler based on these sensors response of air-core LVDT in the prior art, and be not suitable for our acquired Subnano-class, high speed positioning performance than the sensitivity of the improvement sensor of narration here.Also have, these sensors of being narrated in above-mentioned prior art can not utilize us to be incorporated into any of these improvement of our excitation and Signal Regulation electronic device.Desired optimum performance is the LVDT that is comparable to present commercialization in these air-cores LVDT.

At last, traditional LVDT is appeared in the external magnetic field by the strictness restriction equally.Along with external magnetic field increases to some extent, the saturated and LVDT of core becomes invalid.This limitation is by non-traditional designing institute arrangement, and wherein LVDT makes and be operated in (U.S.Patent No.4,030,085) near primary coil and secondary resonance place by non-ferromagnetic body material fully.Yet hereto and other reasons, these limitation of LVDT are in the past shared in this design in its great length scale, also want even littler sensitivity than design in the past.

Depend on rapidly and accurately locate the ability of wisp and instrument at present with nanotechnology in the future.The current length scale is with the 100nm range and dwindles in many manufacturing technologies.For example, the write head in the hard disk drive of commercialization writes the gap routine less than 100nm and there is the pole tip recess to control to tens nanometers.The electric current of SIC (semiconductor integrated circuit) generates and uses 180nm broad gauge mark, moves to 130nm and moved on to 100nm (relevant semi-conductive international technology road figure, 1999 editions) within 5 years in expection within 2 years simultaneously.Only with great difficulty provide enough resolving powers in disc driver and integrated circuit manufacturing, being used to control and check the current sensor that employed lithography process uses for critical dimensional measurement.

Recently experimental work has surpassed big relatively sub-micron scale.These examples comprise the control operation that molecule focuses on people such as () Piner and even individual other atom people such as (for example, see) Crommie.A target of nanotechnology be set up molecule machine (Drexler, K.E.).If constitute this sampling device, they will need the precision positioning of individual atom and molecule.This will need the information on the three-dimensional position of Asia-(dust) precision, when in addition appropriate molecule machine in biological tissue can comprise the response rapidly of several thousand atomic time.

Summary of the invention

An object of the present invention is to provide simple, low cost and high resolution sensor, not careful selection, processing and the processing of the magnetic material that need in LVDT core in the past, use or the Precision Machining of other high resolution position transducers.

Second purpose of this provides high-gain LVDT, do not suffer damage because of Barkhausen noise.

Another object of the present invention provides the insensitive high resolution sensor of temperature variable, and through high permeability core the eddy current heat and do not make itself produce temperature variable.

Of the present invention also have a purpose to provide the very high-resolution force transducer, and it is integrated to be suitable for instrument useful from such resolving power or that require, comprises contour curve analyzer and scanning probe microscopy, as atomic force microscope and molecular force probe.

Finish these and other purposes according to the present invention, have (i) to replace high permeability core to reduce with the low permeability core or eliminates Barkhausen noise, the length scale that (ii) reduces the LVDT sensor is with the raising spatial sensitivity and (iii) improve in the circuit for signal conditioning system.

Description of drawings

Fig. 1 is a prior art, has showed traditional LVDT.

Fig. 2 is the proposition embodiment that the low setting frequency core LVDT of mobile primary coil is arranged.

Excitation and synchronizing signal that Fig. 3 is based on around the analog multiplier are regulated electronic device.

Excitation and synchronizing signal that Fig. 4 is based on around the synchronously simulating switch are regulated electronic device.

Fig. 5 is the function of the output of two secondary coils as core (traditional LVDT) and primary coil (embodiment of proposition) position.

Fig. 6 is the origin of differential Barkhausen noise among the traditional LVDT.

Fig. 7 is the origin of general Barkhausen noise in traditional LVDT.

Fig. 8 is the device that is used for quantization sensing device noise and sensitivity.

Fig. 9 is the LVDT sensor output of showing the suitable optical interdferometer of sensitivity and linear gauging.

Figure 10 is the noise power spectrum of traditional (ferromagnetic core) and air-core (embodiment of proposition) LVDT sensor.

Figure 11 is several traditional and the functions of RMS noise measurement air-core LVDT as the time.

Figure 12 is several traditional and RMS noise measurements air-core LVDT the function as primary coil excitation amplitude.

Figure 13 measures the molecular force probe that uses piezoelectric sensor and LVDT sensor about quantitative individual molecule power.

Figure 14 makes force curve with the molecular force detection to what the LVDT sensor was drawn to piezoelectric excitation voltage and the commentaries on classics of cantilever biography with cantilever deflection on more surperficial.

Figure 15 is the relevant controlling loading force is showed surface imagery contour curve analyzer with LVDT sensor and magnetic driver a prior art.

Figure 16 has the surface imagery contour curve analyzer of air-core LVDT sensor can be used as the power driver that is used to control probe location and loading force equally.

Figure 17 is as above-mentioned identical, and its middle probe is deflection rather than pivotally supported.

Figure 18 is the prior art of showing atomic force microscope.

Figure 19 is based on the X-Y precision positioning step AFM on every side of MFP magnetic head and LVDT sensor, molecular force probe-3D.

Figure 20 is the more detailed view that adopts an embodiment of X-Y steady arm of LVDT position transducer.

Figure 21 is two afm images on diffraction grating.First (A) shows incoherent AFM scanning.Second (B) displaying is used for the image that step moves linearizing LVDT sensor.

Embodiment

Fig. 2 shows our improved LVDT position transducer.This LVDT comprises non-ferromagnetic coil shape (form) 14, the primary coil 15 that moves of coiling around it and two static

secondary coils

3 and 4 be wound on non-ferromagnetic coil shape 10 around.Primary coil shape 14 is to be mechanically connected to relevant object (not shown) with axle 8.Axle 8 can transmit about several microns or the littler order of magnitude displacement of relevant object.Coil shape can be made with any non-ferromagnetic body material, includes, but are not limited to, and does not have the ferromagnet composition, perhaps the plastics of paramagnetic material, pottery and complex.On the other hand, coil shape can be to be made of non-ferromagnetic body bonding agent and coil or a plurality of winding.More complete narration below, excited electrons instrument 11 produces the current drives primary coil.When the position of elementary coil 15 changed with respect to

secondary coil

3 and 4, therefore relevant object was attached to axle 8, and magnetic flux is coupled to two secondary coils to be changed.These voltages amplify with differential amplifier 6 and are transformed into and the directly proportional voltage of core displacement more complete following narration by Signal Regulation electronic device 12.The configuration of this LVDT is moved ferromagnetic material from the live part of sensor.As following discussion, the sensitivity gain that is provided by high permeability magnetic material has been provided in this improvement, but has eliminated Barkhausen noise.The elimination of Barkhausen noise is allowed the level that improves driving voltage 11 and can not cause corresponding increase in output noise, therefore, increases the sensitivity of LVDT.Can notice mobile from the ferromagnetic material of the live part of sensor with reference to the secondary coil advantage.On selecting, material no longer includes any restriction for housing around LVDT (not shown).Because there is not ferromagnetic material in core, the sensitivity of the LVDT of embodiment and noise are insensitive to the external magnetic field, comprise these magnetic fields that produce from case material.

Fig. 3 and Fig. 4 show the excitation and the Signal Regulation electronic device of our improved LVDT position transducer.Two circuit are according to square-wave oscillator 23, therefore provide output in accurate specified amplitude and frequency place.The excited electrons instrument drives LVDT primary coil 15 with pure sine wave.As this purposes, low-pass filter 24 is removed the harmonic wave of the whole square waves on the first-harmonic that uses effectively.Wave filter is best, is stable with respect to temperature aspect variable.High-purity, the low-distortion sine wave that produces is to be amplified by the current buffer 25 that drives LVDT primary coil 15 then.This part terminal result of circuit is the sine-wave oscillator with unusual frequency and amplitude stability.

Fig. 3 shows a kind of pattern of the Signal Regulation electronic device of our improved LVDT position transducer.

Secondary coil

3 and 4 be respectively an end ground connection, the other end is connected to high precision, low-noise differential amplifier 6.When being coupled to Low ESR input source (for example, coil), this differential amplifier is to be designed to produce low noise.The output of differential amplifier 6 is to output to low-noise simulation multiplier circuit 27.The output of wave filter 24 is imported by low noise, accurate phase shift circuit 28 with as other of multiplier circuit 27 and is presented.At last, the output of multiplier circuit 27 comes filtering by another high precision, low noise, stable, low-pass filter 29, to remove the double composition of frequency of multiplier output.The output of this wave filter provides the proportional synchronizing signal in position with the primary coil 15 that moves.On the other hand reference signal is moved on to multiplier 27 mutually, can make signal will move on to current driving primary coil impact damper 25 mutually.In the whole circumstances, the relative phase of primary coil drives and the multiplier benchmark is adjustable.

Fig. 4 shows the another kind of pattern of the Signal Regulation electronic device of our improved LVDT position transducer.Until the output of differential amplifier 6, electronic device is the situation that is similar to Fig. 3.In Fig. 4 circuit, the output of differential amplifier 26 enters into buffer amplifier 31 and inverting buffer amplifier 32.The output of buffer amplifier 31 be fed to the normally closed input of analog switch 33 and the output of inverting buffer amplifier 32 be fed to switch often open input.This configuration is opposite with harmless functionality.The action of analog switch 33 is that square wave is controlled, square wave derives from square-wave oscillator 23, square-wave oscillator 23 comes phase shift by low noise, accurate phase shift circuit 30 before being input to analog switch 33, so two parts of switch are set to when one, and to partially open be that another part is closed.Better, the two-part disconnection of switch 33 and closed 90 degree that exist leave outside the phase of output signal scope from amplifier 26.The output of analog switch 33 is to be fed to stable, low noise, low-pass filter 34.As other patterns, the output of this wave filter provides synchronizing signal pro rata with the position of the primary coil 15 that moves.

Be the primary coil that moving in the basic ideas of any LVDT back with two secondary coils between mutual () feel the function of variation as the position.The upper panel of Fig. 5 is illustrated in the induced voltage and the function of the LVDT that is narrated as the core position of each secondary coil output place of traditional LVDT.Therefore in two kinds of situations, secondary coil is positioned, at the most precipitous these output offsets of part place on the slope of induced voltage.This guarantees to deduct the sensitivity of voltage or mobile as wide as possible initial coil position for variation in core.The response curve of dash lines show two secondary coils in traditional LVDT.The response curve of two secondary coils among we the improved LVDT of solid line illustrated.The sensitivity of LVDT can be to calculate with the output that deducts two secondary coils simply.This is that relevant two kinds of situations are showed in the lower panel of Fig. 5.The sensitivity of the minimum skew of core cooperates straight line to measure around can being used in central authorities around in the central point.In the situation of traditional LVDT, near untreated sensitivity (that is, deducting slope of a curve zero point) is in 3.16 volts/mm and the situation at improved LVDT, and this is 0.26 volt/millimeter.This shows the noticeable advantage of using ferromagnetic core.The magnetoconductivity of core improves gain significantly, increases the sensitivity of LVDT signal.

The limitation that is identified in LVDT resolving power aspect of startability.At least one manufacturer claims that its traditional LVDT has " unlimited resolving power " and is because in Signal Regulation or the defective in showing (the accurate model AB-01 of Lion, Lion Micronics Inc., St, Paul, MN, the U.S.) from any skew of integrality.Thisly claim to be the property flattered advertisement, have two kinds of reasons at least.At first, the coil with the metal wire coiling will be subjected to Johnson (Johnson) The noise.(Herceg，EdwardE.，An?LVDT?Primer，Sensors，p27-30，Jane(1996)，noise)。As a result, Johnson noise is to be present among the LVDT of traditional LVDT and narration here.Johnson noise will be transferred to electric signal in output place of Signal Regulation electronic device, and therefore the actual motion with sensor is difficult to difference.Secondly, introduce the phenomenon of knowing as the Barkhausen noise crowd for the general most important ferromagnetic material that is to use of traditional LVDT.If ferromagnetic core is perfect words, mean magnetoconductivity be constant and the magnetization with linear and level and smooth local formula variation ideally, this phenomenon can be left in the basket and disregard.Yet ferromagnetic material is perfect anything but.Barkhausen noise is in the magnetic state of ferromagnetic material unexpected jump to be named.Defective in ferromagnetic material can cause neticdomain wall by the preferential specific site of pegging.Then, the magnetic domain wall energy removes with heat energy or external magnetic field and pegs.When this took place, neticdomain wall jumped to another metastable state and pegs the position, caused unexpected variation in whole magnetic state of material.

We conclude that in the LVDT sensor electric current restriction is not Signal Regulation or display error aspect the resolving power, but the Barkhausen noise in ferromagnetic core.Because Barkhausen noise often derives from the conversion that Xiao Rong answers magnetic material, flux change can not balance out in each of two secondary coils in variate.This causes the noise in the core position signalling successively.Fig. 6 and Fig. 7 are illustrated in the ferromagnetic core of traditional LVDT Barkhausen and jump and cause locational noise.Fig. 6 and Fig. 7 show the similar elements as Fig. 1, except the core 1 of Fig. 1 draws again, as the polycrystalline material that many defectives and grain boundary are arranged, therefore be that pin is lived neticdomain wall, one of them be considered as being equal to as the 10a among Fig. 6 be considered as being equal to as the 10b in Fig. 7 with another.In Fig. 6, the Barkhausen in little volume materials 10a jumps and enters limit, limit secondary coil 4 than entering the more magnetic flux of the right secondary coil 3 couplings.The generation voltage spike of responding in the on the left side secondary coil is represented with 11a, will represent with 12a greater than the spike pulse of responding in the secondary coil on the right.When these two voltage spikes process differential amplifiers 6 and Signal Regulation electronic device 7, they cause locational noise, represent with 13a.Illustrated in fig. 7 be Barkhausen noise make it be difficult to remove on the other hand.In Fig. 7, the Barkhausen of taking place in crystal grain 10b jumps, and promptly finds out equidistant between two

secondary coils

3 and 4 with chancing on.Because from the jump of the equidistant generation of two secondary coils, equate by the induced voltage spike pulse of 11b and 12b representative.When these Xiao's pulses process differential amplifiers 6 and Signal Regulation electronic device 7, the locational noise that their are offset and do not cause being represented by 13b.

For high sensitivity position measurement in LVDT, the hypothesis that we test Barkhausen noise is the restriction source of noise.As this purposes, noise on our measuring position has following several: the LVDT that (1) is commercial, use is in the primary coil and the ferromagnetic core (Fig. 1) of shipping condition, (ii) Shang Yong LVDT, wherein we change the magnetic state of ferromagnetic core and (iii) commercial LVDT by weak (～10 oersted) external magnetic field being applied to core, wherein we remove ferromagnetic core and replace it with non-ferromagnetic body core shape, and new primary winding of moving of coiling around it, the result is equal to the LVDT of narration here on function.

Fig. 8 shows the noisinessization as these different LVDT, the mechanical hook-up that we use.Constitute by mechanical framework 16, comprise that mechanical flexure 17 adheres to mobile LVDT core 18, or any several traditional LVDT core (Fig. 1) or with the non-ferromagnetic body coil shape of the primary coil coiling of moving.LVDT

secondary coil

3 and 4 is connected to mechanical framework 16, and it is the effect as benchmark.Piezoelectric laminated assembly 19 is pressed on the flexure, and it is moved with respect to mechanical references.In whole measurements that Fig. 8 makes, piezoelectric laminated assembly drive with-15 volts to+15 volts 0.1Hz triangular waves with use Fig. 3 in identical excitation and Signal Regulation electronic device.For each measurement, the gain of Signal Regulation electronic device is adjusted to the sensitivity on the nominal position of 1.3 μ m/v.This sensitivity means that the least significant bit (LSB) (LSB) on our 16 bit data acquisition systems is equivalent to the distance of 0.02nm.

Be the sensitivity and the linearity of calibrating various LVDT, serviceability temperature stable, HeNe (He-Ne) laser interferometer 20 and the traceable calibration grating (calibration criterion, NT-MDT, Moscow, Russia) of NIST-normally used classification in atomic force microscope.Be moved core 18 from the light beam 21 of laser interferometer and reflect away, 22 assemblings of mobile core 18 usefulness retroreflector.By the LVDT response is matched with the interferometer response, we calibrate various LVDT.Fig. 9 shows the result of this assembling, with LVDT (iii) above-mentioned be considered as same, on our the improved LVDT function equivalence and with the measured piezoelectricity B-H loop of methods such as optical interdferometer.The existing scale of LVDT data (solid line) and approaching as far as possible to the skew of coupling interferometer data (circle).As expecting, engagement process is exported the LVDT sensitivity of 1.30 μ m/v.In case after the sensitivity of LVDT has been measured, remove the noise on the measuring position as far as possible.For example, the response of measuring LVDT once, to the infinitesimal displacement of piezoelectric laminated assembly function as the time.

Because they derive from the microscopical distribution of pegging the position in ferromagnetic material,, even also be like this when these cores are made of same material so the details situation that Barkhausen jumps will be all different from the core to the core.And, for the typical LVDT measurement first time, because ferromagnetic core approaches remnant magnetism state, so Barkhausen noise will depend on the details of the magnetic change procedure of indivedual cores.Figure 10 shows the function of the amplitude frequency spectrum of the remanent magnetism that ferromagnetic core and non-ferromagnetic body core LVDT respond as frequency.These frequency spectrums be when static by derive from the measurement noise of the LVDT that discussed radiation and analyze these measurements with Fuli's leaf technology.As shown in Figure 10, the amplitude frequency spectrum of ferromagnetic core LVDT reduces as the function of frequency, and is consistent with the measurement of Barkhausen noise, but not ferromagnetic core LVDT shows and reduces many and more smooth curve.This is absent consistent with Barkhausen noise, but has the Johnson noise of originating in the feedback resistor of Signal Regulation electronic device to exist.Rms noise from 0.1Hz to the 1KHz integration is 0.19nm for non-ferromagnetic body core LVDT and is 2.1nm for ferromagnetic core LVDT.

Ferromagnet often is at metastable state micromagnetism state.These metastable shapes are typically relatively away from ground state.As ferromagnet for various passages being arranged towards ground state is loose.This causes slow relaxation, and wherein magnetic state will little by little change in long-term scale range, typically from several hours to several days, and several weeks and even some months (for example, seeing Bozorth).When the magnetization is lax towards the all-the-time stable state, will change equally to some extent with respect to ferromagnetic magnetoconductivity of disturbance and stability by the external magnetic field.Generally, neticdomain wall will cause relatively small number of Barkhausens to jump gradually towards more rock-steady structure is lax.Figure 11 shows the measurement noise as the function of time about three traditional ferromagnetic core LVDT and three air-core LVDT.The noise of whole three traditional ferromagnetic core LVDT reduces as the function of time, though be not the changeability that has value to consider with smooth mode with among the noise level of each core.Both show Barkhausen noise at observation.During the phase same time, the noise of three air-core LVDT continue be much more constant 0.19nm place roughly with in the middle of three different air-cores, minimum variable is arranged.This expression noise originates from elsewhere: for example, and in excitation or Signal Regulation electronic device.

The increase signal is to increase drive current simply to a method of the ratio (signal to noise ratio (S/N ratio)) of noise.If noise is in some constant value, increases drive current and should increase signal to noise ratio (S/N ratio) simply.Figure 12 shows about the noise of three traditional ferromagnetic core LVDT and three the air-core LVDT curve to exciting current.The air-core noise roughly is inversely proportional with primary current.This response is consistent with the sensitivity that is being limited by excitation and Signal Regulation electronic device.The noise of relevant ferromagnetic core LVDT all has opposite tendency to the drive current curve.When drive current increased, noise equally also increased.This represents Barkhausen noise.When elementary coil drive current increased, it produced bigger oscillating magnetic field, therefore can expel the neticdomain wall of pegging, and caused increasing locational noise successively.In addition, the ferromagnetic core LVDT in Figure 12 and Figure 11 is illustrated in the extremely higher changeability aspect their noiseproof feature.This shows that also noise is the microscopical magnetic variable that derives from each core, i.e. Barkhausen noise.

Should be noted that the LVDT that is narrated can not only be a voltage with movement conversion, but can voltage transitions be motion in opposite mode.One or two these character are used in the following application of the LVDT that is narrated.

Accurate power is measured.Be used for searching power during Figure 13 is illustrated in and measures like this and measure and use the molecular force probe machine apparatus of the LVDT that is narrated.By the deflection of measuring the cantilever of deflection, the situation of this apparatus ergometry when it is pressed into or retracts on sample with sharp-pointed tip 37.High sensitivity deflection measurement mechanism and extremely sharp-pointed tip allow that in the end of deflection suspended wall measurement is until the individual molecule scope.Indentation force is measured equally can be by the suspended wall tip pressure is carried out to the surface.In Figure 13, cantilever 37 is to throw light on low-coherence light source 35.Only focus on cantilever 37 places from this light source with adjustable condenser lens.It is that gather and be directed to position transducer 39 by adjustable catoptron 38 that the light of cantilever reflects away.Position transducer is provided to the controller of instrument (not shown) with voltage, and is therefore directly proportional with cantilever deflection.Whole optics detection system is sealed in the hard stable container 40.This container is through deflection coupling body or

deflection body

41 and 42 and be attached to the framework of instrument 44.These coupling bodies allow containers 40 with respect to the framework 44 of instrument 44 and translation vertically.Piezoelectric laminated assembly 43 is to be used to realize translation and our improved LVDT sensor, is attached to mobile container with the primary coil 15 that moves, and static

secondary coil

3 and 4 is attached to the fixed frame of instrument, and locational information is provided.

Figure 14 is illustrated in the importance of carrying out LVDT sensor in the power measurement.Two panels are illustrated in and use Si (silicon) cantilever (millimicro sensor MESP) to make force curve in the air on mica surface.The A panel of Figure 14 is a cantilever deflection to the curve map of the voltage that is applied to piezoelectricity.Optical track mark 45 is showed curve of approximation and dark track 46 displaying retraction curves.Sticking in the retraction curve between tip and sample is tangible, puts 44 at about 5.5 Fu Chu according to present appearance " sudden turn of events ".There is not same slope as the contact portion that will be noted curve of approximation and retraction curve.This can be that some is classified and explains as tip or sample or both viscoelastic property.Yet it can be interpreted as the artifact of piezoelectricity B-H loop equally, and let us stays uncertainty in explanation.The B panel of Figure 14 is showed the equal deflection data, at this moment draws as the function of the output of our improved LVDT.In this panel, at this moment curve of approximation has identical slope with the contact portion of retraction curve 47, scratches the existence of any Viscoelastic effect in the interaction of tip-sample.Also have, use our improved LVDT sensor to scratch the artifactitious any possibility of piezoelectricity B-H loop in force curve.Second advantage using our sensor is to allow at the X-axis top offset directly to measure (that is, micron unit (as diagram) or nanometer unit).

Surface outline curves is drawn.Draw the traditional LVDT sensor of use in the instrument in various surface outline curves, these instruments comprise the instrument (for example, from the Dektak of Veeco instrument company, Plainview, NY, the U.S.) of many commercializations.Figure 15 shows a kind of such instrument.This is from United States Patent (USP) .4, and Fig. 1 of 669,330 adopts.In this instrument, sharp most advanced and sophisticated 48 to be attached to mobile stylus point 99 be to rotate with pivot around jewel bearing mechanical hook-up 50.The tip be with the contacting of sample 51 in be basis with step 52, therefore scan with respect to the framework of instrument 53.The motion of stylus point assembly is to measure with the LVDT sensor that curve coil assembly 54 and high permeability ferromagnetic core 55 constitute, and therefore moves with the stylus point assembly.Power between tip 48 and sample 51 can use magnetic drive coil 57 be attached to the frame of instrument 53 and change to some extent by magnetic field application is adhered to the stylus point assembly to magnetic filler rod 56.A main idea in this design is with primary coil 55 shielding, prevents the magnetic field that the magnetic filler rod 56 from magnetic drive coil 57 is radiated.Penetrate the magnetic state that magnetic field can change high permeability ferromagnetic core 55 from any assorted of driver, cause position on stylus point assembly 48 tip end surface and/or the variation aspect the sensitivity.

For these instruments that use traditional LVDT, use the LVDT that narrates to allow here and improve the bent property of measuring of profile in essence.Surface profile is drawn when this is included in fair speed and during lower power.And because it may be with our improved LVDT application of force and detection position together, when allowing simplified design, the quality of instrument can reduce with its speed and increase.Figure 16 shows the example that the LVDT of narration uses, and wherein DC current 58 is with 5 additions of vibration primary current through summing amplifier.The insertion of DC current allows along the axle of LVDT primary coil 15 performance power as far as possible.In this embodiment, sharp-pointed tip 60 is to be attached to stylus point 61, therefore motion on jewel bearing mechanical hook-up 50.This whole assembly moves with respect to sample surfaces 51.In the remodeling of this embodiment, LVDT

secondary coil

3 and 4 is driven together with DC current, to increase the power of using.As using the primary coil driver to be performance power,, be possible so this simultaneous power is used and detected because power drive and LVDT sensor driver are very wide separating on frequency.Because the coil shape of the LVDT of narration is made of non-ferromagnetic body material, so do not have influence aspect noise that simultaneous power is used and detection is measured or the sensitivity in the position.

Figure 17 shows that the contour curve analyzer with LVDT another kind of embodiment together, promptly is used as sensor and driver.The element of this embodiment is to be similar to these elements of showing in Figure 16, and except following situation: stylus point 61 is to be attached to instrument 63 (not showing) through the crooked coupling body 62 of deflection in Figure 16.As driver of narrating in Figure 16 and detected electrons instrument, when the high frequency sensors signal was measured simultaneously, secondary coil was driven together equally with direct current power transmission electric current.

Atomic force microscope.Figure 18 shows that atomic force microscope (AFM) is that Fig. 3 place from United States Patent (USP) .Re 34,489 adopts.(atomic force microscope is the device that is used to produce the image of surface topography (with other sample characteristics of for example) to AFM, forms according to the information that obtains from the scanning sharp tip at deflection cantilevered distal end place in the sample surfaces scope.The deflection of cantilever is corresponding to the resemblance of sample.Usually, tip-sample position is that the configuration by the piezo tube scanner fixes, and is forced by the deflection body sometimes.In Figure 18, sample 69 is to use piezo tube scanner 70 to locate in three dimensions.The deflection of cantilever is measured with the optics bar, is similar to shown in Figure 14.These images are drawn as the function of the X-Y position of sample by deflection or other mechanical propertys of cantilever.Instrument can be operated in many different imaging patterns and comprise that mode of oscillation wherein only has the tip to contact off and on the sample surface.Being described in more detail of Figure 18 can be found in referenced patent.

The molecular force probe that Figure 19 shows as narrates together with the AFM functionality in Figure 13.Sample 69 is installed on the accurate X-Y positioning step 71, allow sample under the MFP domination by raster scanning.When its (cantilever) during with the sample surface interaction MFP measure suspended wall deflection, and use various imaging pattern making images.In this AFM, it is such to be unlike in the AFM that narrates among Figure 18, is to be provided by the piezoelectric laminated assembly 43 in MFP along moving of Z axle, therefore from the Z position to the uncoupling of X-Y position.This AFM allows outside conventional Optics in Microscope equipment to aim at the Z axle of instrument equally, and this feature is to be aimed at cantilever tip by the optical aperture in X-Y positioning step 71 72 by external objective lens 73 to express.In this configuration, sample is with respect to MFP and external optical devices and be scanned.Figure 20 shows the sectional plain-view drawing of a kind of embodiment of X-Y positioning step.Promptly use the LVDT of narration so that the information on the precision positions to be provided.Figure 20 is illustrated in the X step 77 of Y step 74 upper supports.The motion of Y step is that the motion mobile and the X step that is attended by Y-axis primary coil 76 is attended by moving of X-axis primary coil 78.These move by Y step and X step

secondary coil assembly

75 and 79 and detect respectively, and (75 and 79) are installed to the non-moving framework of scanner respectively.Optical aperture 72 in the centre of positioning step allows light to enter into sample.

Figure 21 is illustrated in the importance of the LVDT of the narration that generates afm image.Two panels are illustrated in the MFD 3D that is equipped with the X-Y positioning step that shows among Figure 20 and the image of making, and this step uses our improved LVDT.Image uses Si (silicon) cantilever (millimicro sensor MESP) to make in the diffraction grating scope, and using usually is to calibrate AFM by the quadrate array of rectifying, square 5 μ m pits, and nominal 180nm is dark.Making panel A is the measurement of moving as sample with continuous triangular wave and use applied voltage by simple drive pressure electrical scanner.Panel A shows the deformation pattern of diffraction grating pit.They are presented on, and the size aspect was both inhomogeneous also not to make them be presented in the proper array.Panel B shows identical diffraction grating, and imaging at this moment has according to locating from the closed circuit on the basis of signals of the LVDT sensor of narrating.In this image, present uniformity in these pits on the size and have even interval, as desired.Be similar in the molecular force probe their use, the LVDT sensor of narration makes us can critically reappear the image of sample surfaces, by measurement and the correction for effect of piezoelectricity tape and creep effect.

Research with these devices of micron and littler length scale, development and manufacturing have begun and have quickened to some extent.Recently, IBM Corporation has obtained some achievement, and wherein making single atom with the probe of this machine is be positioned from the teeth outwards (probe of scanning tunnel microscope in this case).The accurate orientation of atom, the target of molecule manufacturing will require the inferior Egyptian location of this machine probe in three dimensions.

By these new technologies and device, the non-ferromagnetic body sensor of narrating in it is applicable to desired length scale simplification.The sensitivity of LVDT is and mutual () sense geometry sensitivity In direct ratio.Mutual inductance be with magnetic energy in direct ratio and with square being inversely proportional to of electric current, Number is constant realizes by reducing conductor size if we keep rolling up, and illustrates that so easily mutual inductance and loop length 1 are irrelevant.On the other hand, the derivative of mutual inductance is inversely proportional to loop length,

Therefore, when the LVDT loop length reduced, sensitivity had increased, sensitivity ∝ l ^-1This relation means that LVDT sensitivity only will reach better when loop length reduces.

When the length scale of sensor reduced with these devices, magnetic sensor had another kind of advantage.Magnetic force) magnetic field intensity) scale is l ^-4This means that these power of producing from simple working sensor will help calibration the situation of the non-ferromagnetic body LVDT of MEMs or reduced size.

The embodiment of the present invention's narration only is to consider preferred and explanation notion of the present invention; Scope of the present invention is not to be limited to these embodiments.Those of ordinary skill in the art can make many and various other configurations, and does not break away from the spirit and scope of the present invention.

Claims

1. a displacement transducer is characterized in that, comprise,

Have first and second non-ferromagnetic body coil shape of common axle, each uses at least one winding technique;

Have such winding, the external diameter of its first coil shape is littler than the internal diameter of second coil shape, so each winding can be placed on first coil shape within second coil shape with respect to another;

A coil shape is to move, and another coil shape is static;

Magnetically be coupled to the winding on rest shape or a plurality of winding under the condition of a plurality of windings that inductively are coupled without any ferromagnetic element at the winding on the coil shape that can move or a plurality of winding; With

Electronic circuit produces signal to the relative displacement sensitivity between the coil shape in micron or the scope still less.

2. transducer as claimed in claim 1 is characterized in that, sensor comprises,

There is the coil shape of less external diameter to be wound with two or more windings, and the single winding technique of other coil shapes.

3. transducer as claimed in claim 1 is characterized in that, sensor comprises,

Have than the two or more winding techniques of the coil of large diameter, and the single winding technique of other coil shapes.